The present invention relates to a film-packed battery in which a battery element is stored in a film packing body and a method of manufacturing the same and, more particularly, to a film-packed battery which can appropriately cope with gas generation in an abnormality, and a method of manufacturing the same.
In recent years, strong demands have arisen for lower-weight, lower-profile batteries as power supplies for portable devices and the like. Regarding a battery packing body, in place of a conventional metal can case which is limited in weight reduction and profile reduction, a metal thin film or a laminated film formed of a metal thin film and a heat sealable resin film has been in use as a packing body which can be reduced in weight and profile and can take an arbitrary shape when compared to a metal can case.
As the laminated film, one which includes a metal thin film made of aluminum and a heat sealable resin film made of nylon to form a battery outer surface and polyethylene or polypropylene to form a battery inner surface is generally used. A cathode, an anode, and a battery element made of an electrolyte are stored in a packing body formed of the laminated film. The periphery of the packing body is heat-sealed.
Most of batteries that use metal can case as general packing bodies have a pressure safety valve which, when a gas is generated at the time of an abnormality and the pressure in the battery increases, releases the gas to the outside.
In a film-packed battery which uses a film as a packing body, however, it is difficult to provide a pressure safety valve due to the structure. When an abnormality occurs, the packing body expand to the limit with the generated gas. It is unknown where the packing body may rupture to blow the gas into the equipment, leading to an issue.
Japanese Patent Laid-Open No. 2000-100399 proposes a means with which part of the heat-sealed portion is sealed at a low temperature to form a safety valve. Japanese Patent Laid-Open No. 11-097070 proposes a means with which a non-heat-sealable resin sheet is interposed and heat-sealed to decrease the peeling strength, thus forming a safety valve. With the above means, however, the sealing reliability also decreases in a normal state where the pressure does not increase. Then, the seal portion is deteriorated, and inconveniences such as leakage of an electrolyte may occur. Also, the pressure for opening the safety valve at the time of an abnormality cannot be set accurately. Japanese Patent Laid-Open No. 2001-325926 disposes a scheme of forming a recessed groove in a laminated sheet and releasing the generated gas outside the battery. Even with this proposal, it is cumbersome to form the recessed groove, and the laminated sheet must be welded to an opposing laminated sheet in two steps. Accordingly, very cumbersome operations are needed.